Land mobile radio systems are primarily utilized to provide communications to police officers, fire fighters and other emergency responders, and professional and commercial entities, such as retail store chains, school systems, utilities companies, transportation companies and construction companies, and the like. There are a number of two-way radio systems (also known as land mobile radio systems) that are either presently in use or currently being developed including digital radio technologies that are now available.
For instance, the Association of Public-Safety Communications Officials (APCO) Project 25 (P25) (or APCO-25) represents one effort to set standards for digital two-way radio technology. In general, P25 refers to a suite of narrowband digital Land Mobile Radio (LMR) communication standards for digital radio communications, equipment and systems. P25 standards are produced through the joint efforts of the Association of Public Safety Communications Officials International (APCO), the National Association of State Telecommunications Directors (NASTD), selected Federal Agencies and the National Communications System (NCS), and standardized under the Telecommunications Industry Association (TIA). P25-compliant technology is being deployed in phases commonly referred to as Phase 1 and Phase 2. Phase 2 systems are designed to help improve spectrum utilization. Among other changes to the Phase 1 standard, the Phase 2 standard proposes migration from Frequency-Division Multiple Access (FDMA)-based channel access scheme to a Time-Division Multiple Access (TDMA)-based channel access scheme. Further details regarding the P25 standards can be obtained from the Telecommunications Industry Association, 2500 Wilson Boulevard, Suite 300 Arlington, Va. 22201.
Mobile Repeater Systems (MRSs)
Land mobile radio systems typically include portable subscriber units (SUs) and a base station, and in some cases additional mobile repeater systems (MRSs). To explain further, a SU is usually sized so that it can be easily carried by a user. As such, SUs are typically powered by a small rechargeable battery, and have a relatively small antenna due to size constraints. For those reasons, SUs are generally designed to transmit at a relatively low power, and therefore, the operating range of a SU is limited. To overcome the range limitations associated with portable SUs, a communication system can often include one or more mobile repeater systems (MRSs).
A Mobile Repeater System (MRS) is a radio system component that includes a high-power mobile radio unit that can be used to extend radio coverage area of a fixed system, such as a trunked radio infrastructure. For example, MRSs are currently used in radio communication systems to provide coverage to portable subscriber units (SU) in areas where the coverage provided by the fixed system is insufficient. For instance, a MRS can be used when radio coverage to portable SUs is poor or would otherwise be unavailable (e.g., SUs that are in a marginal coverage area). In operation, a MRS can receive RF signals being transmitted to or from a portable SU, amplify these RF signals, and retransmit these signals at higher power to increase the range of the communication system, thus enabling an extended communication range for the portable SUs. Preferably, such range extension is automated such that when a portable SU is within communication range of a MRS this range extension takes place and the portable SU is able to communicate a greater distance. By deploying an MRS, the SUs can be distributed over a wide geographical area.
In one deployment approach, a MRS can be a fixed unit that is deployed at a particular location to extend coverage in a fixed area. In another deployment approach, a MRS can be implemented within a transportable unit (e.g., suitcase) that can be transported by a user. In a more common arrangement, a MRS can be installed or mounted in a vehicle that can be deployed to different regions, and can provide repeater capability between portable SUs and a base station. In any of these deployments, the MRS is powered by a power system in which battery life is generally not a concern (in comparison to batteries used with portable SUs), and can transmit at a higher power level. The MRS can also include a relatively larger antenna (in comparison to those used with portable SUs) that improves transmission and reception efficiency. In some implementations, the MRS may also include multiple antennas (e.g., diversity antenna structures) that increase transmission and reception reliability.
SUs within proximity of the vehicle having the MRS can communicate amongst one another on a single channel provided by the MRS. To explain further, an MRS typically consists of a mobile trunked interface (MTI) that is physically connected to a repeater interface (RI). The MTI provides the radio communication to fixed network equipment (FNE) on the fixed system, and the RI interfaces to the SU on a conventional channel for providing talk groups. Multiple SUs can use a single MRS for creating a talk group at any time if the SUs are all on the same channel. However, the MRS can provide only one physical channel of communication at a time, and therefore can only support one talk group at a time. In other words, although the MRS can support more than one talk group, because there is only one channel available, only one active talk group conversation can be supported at one time. The other talk groups have to wait until the channel is freed.
SUs can operate in various modes. For instance, SUs can communicate directly with each other in a “talk around” mode without any intervening equipment between two SUs, or in a conventional mode where a requesting SU chooses the channel to talk on and two SUs communicate through a repeater or base station without trunking. In addition, some modern systems use a trunking protocol that allows multiple users and groups to share one or more frequency channel pairs (e.g., a pool of channels). In a trunked system, a repeater or base station can provide a control channel that individual SUs monitor and use to request a frequency channel to transmit on. Two radios may communicate in a trunked mode where infrastructure equipment dynamically assigns the requesting SU a channel to talk on and traffic is automatically assigned to one or more voice/traffic channels by the repeater or base station. This protocol allows multiple talk groups to share a group of frequencies without interfering with one another. In this regard, it is noted that in a conventional system, the talk groups that share a channel must wait for the channel to be idle before starting a conversation, and even if there is another “open” MRS present at the site, there is no way to inform the SUs (that belong to a particular talk group) that they should use a channel provided by the open MRS.
Multiple MRSs
In many cases, multiple MRSs can be deployed at the same site or incident scene. Each of the MRSs are configured to operate as a single frequency repeater. Because each MRS is only capable of providing one physical communication channel, the multiple MRSs can only support one talk group at a time. In other words, since there is only one physical channel on a MRS, only one of the talk groups can use that channel at any particular time.
In situations where multiple MRSs are deployed to a site in proximity to each other, the multiple MRSs may interfere with each other if they operate at the same time. To avoid such interference, it is common for one MRS to be designated as a master that remains active, and for the other MRSs to be designated as slaves that simply repeat radio communication for the master. One approach for doing so is disclosed in U.S. Pat. No. 7,711,319, entitled “Method and System for Distributing Talk Group Activity Among Multiple Vehicle Repeaters,” assigned to the assignee of the present disclosure, its contents being incorporated herein by reference in its entirety.
However, with this approach, some of the communication resources of the slave MRSs are not utilized. In addition, his approach does nothing to eliminate contention between two talk groups assigned to one MRS.
Notwithstanding these advances, there is a need for improved methods, systems and apparatus for utilizing multiple MRSs when they are deployed at a same site.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present disclosure.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.